The present invention is directed to a sealing device for a pressure case used in a rotary machine, especially for a machine fabricating corrugated board.
In a machine for fabricating corrugated board, a sheet of cardboard is fed into a pair of superimposed corrugating rollers, which rollers are rotating in opposite directions and cause a corrugation of the cardboard sheet. Glue is applied or coated on the top of the flutes of the corrugated cardboard sheet by means of a gluing roller as the sheet is being held in contact with the lower corrugating roller. Thereupon, a glue-coated cardboard sheet is provided with a covering sheet by means of a pressing cylinder, which is running also in the opposite direction with regard to the lower corrugating roller.
In order to achieve a good quality of the cardboard produced, it is essential to keep the sheets thus corrugated in permanent contact with the corrugating flutes of the lower corrugating roller during the application of the glue and until the covering sheet has been pressed against the corrugated sheet, for example, by a lower pressing cylinder. A presently used solution consists of encasing the gluing device as well as the rear part of the lower and upper corrugating rollers and the pressing cylinder in a case within which additional pressure is to be built up with a view of having the paper pressed against the corresponding rollers or cylinders. This solution involves the problem of tightness throughout the length between the rotary cylinder and the opposite lateral edges of the case.
According to the presently used solution, the case parts are arranged opposite the pressing cylinder including a wall having the shape of a cylinder portion joined at its lower edge with an axle situated underneath the pressing cylinder. This wall is supposed to envelope the pressing cylinder almost as far as the point or line where it is in touching contact with the corrugated rollers. The wall has the shape of a cylinder portion and is strengthened by vertical arc-shaped ribs and/or horizontal cross members. The wall can be moved toward the pressing cylinder by pressing means, for example, shifting spindles. In order to achieve the tightness and sealing in the area, the upper edge of this wall is extended by means of a lateral tongue of a flexible material, such as a material sold under the trade name "TEFLON". This tongue is oblique and turned outwardly with regard to the wall. In this way, when the wall is moved toward the pressing cylinder, the flexible tongue will tangentially touch the pressing cylinder very close to the touching line between the cylinder and the lower corrugating roller shortly before the covering sheet will contact the corrugated sheet. The additional air pressure built up within the case is then expected to press the flexible tongue to a certain extent against the pressing cylinder, thereby improving the seal or tightness of the case.
However, practical use has revealed that this tightening or sealing tongue undergoes uneven wear over its whole length, thus, entailing non-neglectable losses of pressure. Therefore, the sealing tightness is unreliable. Turbulent air might accumulate on either side of the tongue close to the rotary cylinder and, thereby, cause the tongue to vibrate and to emit intense whistling noises, which are particularly annoying for the operators working close to and around the machine.
In a similar way, the upper lateral case edge is arranged opposite the upper corrugating roller and includes a lateral plate fitted on joints or pivots and directed obliquely downward. The plate carriers throughout its length a tightening seal shaped as a lateral bar of Teflon material. In this way, if the plate is lifted by underlying means, it is possible to apply the Teflon sealing bar against the corrugations of the upper roller. Springs included in the lifting means enable small diameter variations of the corrugating roller due to the corrugation types or structure. The bar also has a certain width and a curved contact surface for allowing to compensate for small translatory movement of the upper corrugated roller with regard to the lower corrugated roll. This translatory movement is inherent to the function of the machine.
As may easily be understood, the hardness of the Teflon necessary for insuring tightness is unable to reduce noisy vibrations caused by the bar rubbing against the corrugations. Moreover, the uneven wear of the contact surface also causes undesirable pressure losses.